Interpretive Summary: This is a Germplasm Release, no Interpretive summary required.

Technical Abstract:
The Agricultural Research Service of the United States Department of Agriculture announces the release of a novel watermelon breeding line. This novel line, designated 'USVL-200' contains the nuclear genome of watermelon cultivars (Citrullus lanatus var. lanatus) and the chloroplast and mitochondrial genomes of the desert species Citrullus colocynthis. USVL-200 produces a high number of female flowers (one female flower for every 5 to 7 male flowers) as compared with typical watermelon cultivars (one female flower for every 6 to 10 male flowers). USVL-200 was developed by Dr. Amnon Levi, Research Geneticist; Dr. Claude E. Thomas, Research Plant Pathologist; Dr. Judy A. Thies, Research Plant Pathologist; and Dr. Alvin M. Simmons, Research Entomologist at the U.S. Vegetable Laboratory, and Dr. Anthony P. Keinath, Professor of Plant Pathology at the Clemson University Coastal Research and Education Center, both in Charleston, SC.
Efforts to develop USVL-200 were initiated in 1999 with the greenhouse evaluation of plants derived from reciprocal crosses between watermelon cultivars (C. lanatus var. lanatus) or U.S. Plant Introduction accessions (PIs) of C. lanatus var. citroides and PIs of the wild desert species C. colocynthis. In the 1999 evaluation, all F1 plants derived from crosses where either C. colocynthis PI 386015 or PI 386016 was the female parent resulted in all F1 plants that produced one female flower for every 2 to 4 male flowers. In contrast, when the watermelon cultivars Charleston Gray or New Hampshire Midget (C. lanatus var. lanatus) or C. lanatus var. citroides PIs were the female parents, the F1 plants produced one female flower for every 5 to 9 male flowers. These results raised the possibility of a maternal (cytoplasmic) effect on female flower production in watermelon, because chloroplast or mitochondrial genomes that are maternally inherited in plants may play a role in female flower production in watermelon.
USVL-200 was produced by first crossing a F1 hybrid ['New Hampshire Midget' (C. lanatus var. lanatus) x Griffin 14113 (C. lanatus var. citroides)] with C. colocynthis PI 386015 as the female parent. Then, most of the nuclear genes of the hybrid plant were replaced with nuclear genes of cultivated watermelon (C. lanatus var. lanatus) through repetitive backcrosses with watermelon cultivars including 'Allsweet', 'Charleston Gray', 'Minilee', 'Allsweet', 'Charleston Gray', 'Black Diamond' 'New Hampshire Midget', and 'Black Diamond'. A BC8-plant was self-pollinated for four generations to produce USVL-200.
Our experiments with DNA probes confirmed that USVL-200 contains most of the nuclear genome of the cultivated watermelon C. lanatus var. lanatus and chloroplast and mitochondrial genomes of C. colocynthis. USVL-200 has unique fruit characteristics including globular fruit with a dark green rind, similar to that of 'Black Diamond'. However, USVL-200 has yellow-pink flesh, while 'Black Diamond' has dark red flesh. The fruits of USVL-200 mature and are ready for harvest in early to mid-season, similar to 'New Hampshire Midget'.
USVL-200 is recommended for use by scientists and plant breeders who are interested in studying effects of foreign cytoplasm (chloroplast and mitochondria) on photosynthesis, respiration, disease or pest resistance, flower production, and fruit quality in cultivated watermelon. USVL-200 can also be used for enhancing watermelon germplasm, and in studies of lycopenes versus carotenoid production in watermelon.
Small samples of seed of USVL-200 are available for distribution to interested research personnel and plant breeders who make written request to A. Levi, U.S. Vegetable Laboratory, 2700 Savannah Highway, Charleston, SC 29414-5334. Seed of USVL-200 will also be submitted to the National Plant Germplasm System where it will be available for research purposes, including the development and commercialization of new cultivars. It is requested that appropriate recognition of source be given when this germplasm contributes to research or development of new breeding line or cultivar.